The Story of the W-670 Replacement Pistons

The Story of the W-670 Replacement Pistons

In the last issue of Flying Wire, Air Repair gives their updates, news and notes on page 12. Stearman owners will see that the new production STC W-670 pistons are listed. As of this point, the STC has been transferred from Olde Thyme Aviation, Inc. in Seattle, Washington to Air Repair, Inc. who will keep this piston available to the entire Stearman community indefinitely. But there’s a heck of a story behind this piston beyond simply replacing a part who’s supply was running out.

To get up the nerve to embark on the arduous FAA process, there has to be a “business motivation” which will at least pencil out to justify the amount of funds needed to take a new part through the entire FAA process. Nobody in their sane mind is going to put a hundred thousand dollars into building a new piston if it looks like it will take 100 years to amortize the investment in the number of pistons to be sold going forward. I wasn’t eager to be anointed with this title.

In our case, at Olde Thyme Aviation, we are running six W-670 engines at the Museum of Flight at Boeing Field in Seattle. We use a PT-17, and N2S-4, two Waco UPF-7s and a 1927 and 1929 Travel Air. Typically we have to rebuild one engine per year. When Larry Lujan, our engine rebuilder at Gold Coast Aviation in Salinas, California told me that he was out of NOS stock and nearing the end of his +.10 OS pistons, I began to sweat. I looked everywhere for NOS pistons but those that were left were being hung onto like gold. Sure, I found partial solutions such as milled down 4180 pistons from the famous W-670-23 (constant speed) from the Cessna 190 days. Others told me that they simply turned the ring grooves deeper and used thicker rings to keep using the same pistons. It was obvious to me that many pistons out there are being used over and over beyond max/min tolerances. But here we were using the planes for Part 91 Commercial Scenic Flights. One accident with an NTSB engine teardown which might reveal any part not within specs and I might as well kiss off any chance of insurance protection.

The only solution out there seemed to be turning to Air Repair to do the Jacob’s conversion but I would have to give up the originality of the Continental and it was nearly $ 25,000 per engine. With six engines to be replaced, this sent my target of what I would have to spend as high as $ 150,000. Thus, our “business decision” to pursue this project was born. If we could take this project to completion for anything less than this target price and end up with new pistons for everyone, it could be justified economically. So the idea was brewing in my mind continuously for several years. The additional challenge of having other enthusiasts tell me “It couldn’t be done” only challenged my mountain climbing background even more.

I had heard that the entire inventory of the Precissi Brothers Spray Service in the Southern San Joaquin Valley had been purchased by Air Repair. I thought” Oh yeah, I can perhaps get a few more pistons to keep operating a few more years.” I couldn’t even get Pete Jones on the phone the first few times—I think that’s how many people had been bugging him about pistons for years. I finally got him on the phone by complaining that I had inherited an engine years back that he had done some work on and wanted to speak to him about it personally. When I pursued getting any pistons from him, he groaned and told me that that it was totally hopeless, that he had been on Continental’s case since the 1980s to do a run and that they had reneged on an offer to take an order due to the lawyers saying the liability was too high. In this conversation I told Pete I was seriously planning on having a go it ift because of the economics of having to face engine conversions otherwise. His tone of voice picked up a bit and he said he’d be glad to loan me his files on all the channels he had pursued previously in his own effort if I was truly serious about pursuing it.

Within Pete’s files were letters to many engineering firms and a purchase order to Continental which was never filled. Before trying to “reinvent the wheel,” I consulted with an attorney and fired off a letter to Continental suggesting that the liability of not providing either the blueprints or replacement availability was perhaps a stronger liability than providing new pistons. Never got a response.

I dropped off the pistons at a metallurgical analysis company to find out what alloy the original were made from and made an appointment with the Seattle Aircraft Certification Office. What an experience this was. I discovered why everyone I had ever talked to about the possibility of making pistons had always said “you’ll never get it through the FAA.” Here were some wonderful people at various levels consistently telling you that you couldn’t get it done…you can’t do this and you can’t do that. Well it turns out that they are used to being pounded on by so many people with good ideas who simply do not have the funds to pursue the idea to completion. They want to see that the individual with the idea truly has the money behind it before they’ll give you any type of support. Once I explained that it was cheaper to go ahead and see a project through than to face the alternative, they became much more helpful. But, they had obviously been well trained to try and chase the people out who had good ideas but no funds to pursue them. This “skepticism” runs rampant in all departments of the FAA that I had contact with, including the DER (Designated Engineering Representative). However once the DER fully understood that we were committed to spend the money to take it to completion, he became our champion at the FAA. And this is probably the most important item we learned beyond showing the FAA that you’re prepared to spend the bucks. You simply don’t have a chance unless you have a known DER working with you who already has an acceptance at the ACO office on prior work. Without our DER, Tom Moreland, we never would have even gotten through the blueprint stage.

The original alloy turned out to be 2018 aluminum which has a very high nickel content. And it was here that I began to suspect that Continental’s reluctance to take Pete Jones’ order in 1987 wasn’t really due to liability concerns at all. It was purely economics. Alcoa isn’t willing to make a meld of 2018 aluminum at any of its foundries unless they get a minimum, order of 80,000 pounds. That’s 40 tons folks! Can you figure out how many pistons that would make? That’s wartime volume! Alcoa taught me that the nickel has to be reclaimed from each “filter” that the meld goes through repeatedly which makes it very costly and very time consuming. I think that Continental realized that they couldn’t resurrect the original alloy for the pistons that was certified for the engine and didn’t think that the demand was high enough to justify going through the work we went through on a new alloy. At this point, I’m convinced that their failure to respond to Pete’s order was simply an economic decision.

So we turned to an alloy that is widely used today which is the 4032 alloy used on the Pratt and Whitney 985 engine and on locomotives. Both of these engines produce much greater heat and stress than the W-670.

Now I had to figure out who I could use to engineer the pistons. I had called three Boeing engineers but had no luck. I had a “near bite” from one of them but he wanted a commitment of $ 35,000 to do the project with funds up front. The attitude here was one of “you need me more than I need you.” And this totally turned me off. I’m used to the Stearman folks who’ll just about give you the shirt off their back if you’re passing through town and won’t let you even buy your own gas. I didn’t need an attitude like this.

Within our flying community is an extraordinary individual originally from Columbia named Guido Perla. Guido is a self made man who started with nothing but his engineering degree and is now one of the world’s foremost ship designers. Today he has full architect, design and engineering firm right on Boeing Field due to his personal love of vintage airplanes. He has been meticulously restoring a Cessna 170-A and is co-owner in a Beaver. I showed him the project and asked him if he would be willing to meet the DER. Now Guido loves radial engines and can flutter his epiglottis in an incredibly accurate imitation. He embraced the project fully as his “willingness to make a contribution to aviation” that would be remembered long after his passing. He never discussed price and never presented me with an invoice. So when he disassembled his Cessna 170 for a complete restoration and could no longer commute to work, I purchased a 170-B that a pilot at our local grass strip had to sell due to family hardships for $ 35,000 and “loaned” it to Guido for two years. I figured I could always sell it later (which I did two months ago) and get the exact same amount of money back. The engineer was tickled to death to have a plane to use free for two years and it allowed him to get his project finished. A win/win for everyone involved. I spent the same amount of money that the Boeing engineer wanted, got the job done first class, the engineer was happy with the arrangement and then I got the money back when I sold the plane.

Part of the engineer’s challenge was to design the pistons for a different “thermal coefficient” for the 4032 alloy. Because this alloy doesn’t expand as much as the original 2018 alloy, the new piston is intentionally engineered .002 wider in outside diameter so that at full engine heat, the pistons occupy the same amount of space and is the same size as the 2018 original alloy piston. The added benefit here is that when the engine is cold the new piston works better to prevent too loose a fit or piston slap. The ring grooves are designed so that the same ring kit and piston pin from the original standard piston fit properly on the new piston.

From project conception to the time we were able to follow the necessary steps and do the required engine block run, it took nearly 2 ½ years and nothing was left unattended. It was tedious and required a tenacious patience in working with the FAA to okay one step before going onto the next. Once gain, the only reason it worked is because we were working with Tom, the DER , whom the FAA ACO already accepted as knowing their procedures and standards that were acceptable. The DER charged $ 75 an hour and we spent about $ 15,000 with him. He gave us a special rate when he traveled down to Salinas, California on three occasions to work with Larry Lujan at Gold Coast Aviation; prior to doing the block run; at the commencement of the block run; and again at the conclusion of the block run. Tom got genuinely excited about the project and became as much of a team participant rooting for the thing to get through as Guido, Pete and Larry.

The block run was a major event in itself. Larry Lujan has been working with W-670s for nearly 50 years and actually pioneered the use of the roller bearing replacement which has eventually been adopted nationwide. By the way, we used this engine block run to also STC an improved roller bearing that uses a “bronze” cage instead of steel so that rust can’t develop on the race that holds the roller bearings!

Our choice was either to change an aircraft to “restricted category” and fly 500 hours on the test pistons, or to do an engine block run for 150 hours at settings which would make you wince. I chose the engine block run because I was warned it might be difficult and frustrating to get the plane back in normal category after changing it to restricted. Plus flying the plane for 500 hours would have taken a far longer time than what Larry Lujan was able to do working on the ground.

Larry mounted the engine on the back of a flatbed pickup with all the harness, gauges, oil and fuel tanks that one would have in a plane. We also had to secure the use of a Beech electric prop to be able to simulate the stress on the engine for takeoff, different manifold pressures and RPMs. This engine screamed on the taxiway at Salinas Airport in the far northeast corner of the field. It consumed $ 6,200 dollars of aviation fuel. Now imagine exactly how long 150 hours is. That’s like being out there next to a screaming engine for 8 hours a day for 5 days a week for 3 ½ weeks. But you can’t simply start it up and walk away until it needs gas. You have to stand right next to it and adjust the engine RPM settings every two minutes for half the test and every five minutes for half the test per the FAA testing requirements which you can read adjacent to this article. What Larry Lujan accomplished for Stearman owners and other aircraft owners that use the W-670 engine is more than I can imagine anyone else ever being willing to perform. And he did it in only four weeks. His excitement level was that strong! But the guy lives and breathes the W-670 engine and, just like the engineer, wanted to be a part of keeping history alive.

The entire effort was a collaborative one between Olde Thyme Aviation, Pete Jones at Air Repair, Larry Lujan at Gold Coast Aviation in Salinas, California, Guido Perla the engineer and Tom Moreland the DER, all of whom were stepping up to the plate to accomplish whatever it took to keep the ball rolling. The momentum and excitement even spilled over to the head of the ACO, Dick Simonson, who accompanied the DER down to Salinas for the engine tear down and inspection after the block run. However it never would have even started had it not been for many of the Stearman owners from the Southeast whom I met at Galesburg 2000 and encouraged me to go ahead with this and that they would be willing to buy the replacement pistons.

When we disassembled the engine in front of the FAA representative from the ACO and the DER, only one single piston showed about .0005 of wear on one of the four ring lands. It was remarkable. These pistons took everything that the intentionally abusive block run could throw at it and looked perfect at the end of the test run. Run your own airplane at stresses such as what you see on the test run requirements and you’ll cringe! We actually broke the Beech electric prop at 105 hours and had to get another one to finish the block run.

Just when I thought I had everything “whipped,” I learned that the PMA process was going to be a bureaucratic process similar to the STC. But this time the DER would not be able to help me. Now I needed a relationship with something called a DAR. Wow, what’s this? I called up three DARs to get help building a quality control manual but none of them were interested. Pension fund payments from Boeing in retirement were plenty generous and they didn’t need the work. I called the MIDO which is where you have to go to get a PMA certification to have something made which you’ve already broken your ass on to get an STC. Turns out there are twenty five people in this office and each one will tell you differently what they want to see in a QC manual. And when I called the one up I was assigned to, he was the new kid on the block and was absolutely ROTE on his procedure. Even when I made two attempts at a QC manual by virtually copying other approved manuals that had been approved at MIDOs in other regions of the country, I couldn’t get it through. There is simply no consistency which I could perceive from one region of the country to another nor is there consistency from one individual to the next within these departments. (Strong opinion here salted with frustrations!)

So far, the project cost about $ 100,000 broken down as follows:

$ 20,000 for test engine

15,000 fuel and labor for test run

35,000 engineering

15,000 DER consultant

15,000 tooling/dye

As part of the “business decision” to pursue this project, I rationalized that I had to spend the $ 20,000 on the engine anyway and the $ 35,000 was recoverable if I sold the airplane which I had bought for the engineer to borrow……which I did. However, I was at the end of my rope having spent all this money to get the STC to now find another road block which I had made two attempts to get through. In the meantime there were all these calls from guys saying “You don’t need a PMA if you have an STC.” Right….get a life! As if I hadn’t been totally indoctrinated in what the rules and procedures are. Then Pete Jones tells me that some guy shows up at Galesburg 2002 with pistons he made in an auto machine shop to put in his engine saying “Why not just do this? Here’s all you have to do!” That’s about as legal as passing out narcotics to kids for free at the pharmacy. Gees fella…………………

So I turned to Pete Jones who already had his parts for the Jacobs engine PMA’s which he’d been having manufactured. Air Repair made me an incredible offer to cash me out of the “hard dollars” I’d invested if I subtracted the engine that I had to build anyway and the airplane cost which I was able to sell later. I didn’t count my personal time in the project which I estimated at about 300 hours over three years. But who gets to pay themselves anyway? It’s like Dudley Moore in his famous quote in Arthur. “But I’m my own boss and I get to take Sunday’s off.” I didn’t count my personal time because I had to come up with a business solution as an alternative to having to convert the six engines at a potential outflow of $ 150,000. Air Repair graciously took over the PMA efforts with a promise to keep the country supplied going forward with the replacement pistons for the W-670. I’m looking forward to continuing to rebuild my engines indefinitely for use at the Museum of Flight so that they never have to have a power plant on them that wasn’t original. This originality doesn’t’ extend to the Travel Airs, of course, but I haven’t seen many other scenic biplane ride businesses operating these days with OX-5s or Hispano Suizas, have you?

By Ken Horowitz|
2016-11-13T09:33:33+00:00 August 23rd, 2003|Flying-Wire|Comments Off on The Story of the W-670 Replacement Pistons

Stearman Restorers Association

The Stearman Restorers Association is an independent “Not for Profit” 501C-3 Corporation that is dedicated to the preservation, restoration, flying and safety of Stearman Aircraft through the education of both members and the public. The Stearman was a primary trainer for both Army and Navy cadets in WWII.